Novel splicing method

ABSTRACT

Disclosed herein is a method for splicing the ends of thermally stable fibers, filaments, strands, wires, etc., which comprises applying a thermally stable imide-forming polymer to the ends to be spliced and then converting the imide-forming polymer to a polyimide.

United States Patent [72] Inventor Raymond J. Enos Springfield, Mass. [21] Appl. No. 694,791 [22] Filed Jan. 2, 1968 [45] Patented Sept. 21, 1971 [73] Assignee Monsanto Company St. Louis, Mo.

[54] NOVEL SPLlClNG METHOD 8 Claims, No Drawings [52] U.S. Cl 156/158, 156/157, 156/331 151 Int. Cl B65h 69/02 [50] Field 01' Search 156/157, 331, 158

[56] References Cited UNITED STATES PATENTS 3.179,633 4/1965 Endrey 156/331 UX Primary Examiner-Carl D. Quarforth Assistant Examiner-Brooks H. Hunt A!l0rney.r-William J. Farrington, Arthur E. Hoffman and H.

B. Roberts ABSTRACT: Disclosed herein is a method for splicing the ends of thermally stable fibers, filaments, strands, wires, etc., which comprises applying a thermally stable imide-forming polymer to the ends to be spliced and then converting the imide-forming polymer to a polyimide.

NOVEL SPLICING METHOD The invention herein described was made in the course of or under a contract or subcontract thereunder with the Departmeng of the Air Force.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for splicing thermally stable fibers, filaments, strands, wires, etc. More particularly, this invention relates to a method for splicing thermally stable fibers, filaments, strands, wires, etc., which comprises 1. bringing the ends to be spliced into a proximate position with respect to each other, 2. applying an imide-forming polymer to the ends to be spliced,

3. curing the imide-forming polymer to a thermally stable polyimide.

2. Description of the Prior Art The splicing of fibers, filaments, wires, strands, etc. is well known in the art, dating back in some instances to ancient times. However, modern technology has provided novel fiber and filaments such as boron, carbon, graphite, refrasil, quartz, etc. which present a special splicing problem. Thin filaments of these materials are susceptible to breaking during their manufacture, during wind up operations, during coating operations in conventional coating and/or sizing operations, or during their use or applications. The breaks in the abovementioned filaments cause excessive delays involved in splicing the broken ends. Conventional splicing means such as tapes, clamps, etc. are unsuitable for obvious reasons of thermal instability, added bulkiness and cost. Moreover, the fragile nature of some of the above-mentioned fibers and filaments makes it impossible to knot or twist the broken ends together.

Attempts have been made to splice broken ends of the filaments described above using thermoplastic and epoxy-type adhesives. However, these materials require long setting times in order to cure the adhesive. In addition, such adhesive materials are thermally unstable.

If the break occurs during a coating operation involving high-temperature cure, such as a wire tower-coating operation where the elevated temperature zones reach temperatures as high as 400 C., a special problem arises. When a conventional adhesive bonded splice is subjected to these high temperatures, the adhesive used to make the splice usually fails while the wire is in the high-temperature zone of the tower causing added problems such as extended down time, cooling problems, etc.

A definite need exists in the art for a splicing method which will provide rapid splicing and a spliced joint which will withstand high temperature without the need for prolonged aging of the spliced joint.

The present invention solves the above mentioned splicing problems by providing a convenient method for obtaining a rapidly made, high-temperature resistant splice, without resorting to the use of undesirable tapes or clamps or impractical twisting or knotting operations, or to time-consuming gluing operations.

SUMMARY OF THE INVENTION 3. curing the imide-forming polymer to a thermally stablepolyimide.

The advantages of the present invention is that it provides a process for the rapid splicing of thermally resistant fibers, filaments and other related materials, wherein the splice maintains its strength even upon exposure to high temperatures.

The present invention solves'problems widely encountered in the splicing of high-temperature-resistant fibers such as the long setting times required by conventional adhesives and thermally unstable adhesive bonds which fail at elevated temperatures. Moreover, the present invention eliminates the need for tapes and clamps and provides a splicing technique for materials which are not readily adaptable to being twisted, braided, tied or knotted.

For purposes of this application the term filament will be used to include fibers, threads, filaments, wires, slender rods, strands, etc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is applicable to the splicing of high temperature-resistant filaments such as those filaments prepared from boron, carbon, graphite, quartz, refrasil, glass, asbestos, nichrome, copper, tungsten, aluminum, and other related materials.

The imide-forming polymers used to prepare the thermally stable splice include polyamide acids prepared from aromatic tetracarboxylic acid dianhydrides and derivatives thereof and polyamino compounds containing at least two primary amino groups per molecule. In a typical example of the preparation of these polyamide acids, equimolar amounts of compounds such as benzophenone tetracarboxylic acid dianhydride and 4,4'-oxydianiline are reacted in N-methyl pyrrolidone at temperatures of under 60 C. to form an imide-forming polymer. Upon further heating of this polymer at elevated temperatures the polyamide acid is converted into a thermally stable polyimide. These polyamide acids which are based on tetracarboxylic and polyamino components and which are used in the present invention as the imide-forming polymer are described in detail in U.S. Pat. Nos. 3,179,614, 3,179,633, 3,179,634, 3,179,635, 3,190,856, and 3,277,043 which are incorporated herein by reference.

Also suitable as the imide-forming polymer component of the present invention are those polymers prepared by the reaction of a monoacid halide of a tricarboxylic acid monoanhydride and a polyamino component containing at least two primary amino groups per molecule. In a typical example of the preparation of these types of compounds, equimolar amounts of the monoacid chloride of trimellitic anhydride and methylene dianiline are reacted in N-methyl pyrrolidone at temperatures below C. to form an imide-forming polymer. Upon further heating at temperatures above C. this polymer undergoes imide formation. These polymers prepared from monoacid halides of tricarboxylic acid anhydrides are described in detail in U.S. Pat. No. 3,260,691 which is incorporated herein by reference.

Also suitable as the imide-forming polymer component of the present invention are those polymers prepared by the reaction of a tricarboxylic anhydride with a diphenol diester type compound as is described in detail in British Pat. No. 1,070,364, which is incorporated herein by reference.

Also included as the imide-forming polymer component of the present invention are those polymers which are capable of being converted to thermally stable polyimide-type structures which are generally well known to those skilled in the art.

The following examples are set forth in illustration of the present invention and are not to be construed as limitations thereof. All parts and percentages given are by weight unless otherwise indicated.

EXAMPLE 1 This example is set forth to illustrate the use of an imideforming polymer to splice the ends of a boron filament having a diameter of 4 mils, which filament broke while being coated in a wire-tower-coating operation. The ends of the boron filament are brought into overlapping contact with each other and a small amount of an imide-forming polymer solution is applied to the overlapping ends. The solvent for the polymer is ignited and then the flames are quickly quenched in order to accelerate the drying of the polymer, i.e. the evaporation of the solvent and the conversion of the polyamide to a polyimide. A strong splice results within 1 minute and the spliced filament is immediately conducted through the elevated temperature zones of the wire tower where the temperature reaches 400 C. under moderate tension. The splice withstands the elevated temperatures without softening or parting. Approximately 2 minutes elapses between the time when the broken ends are first overlapped and coated with the imide-forming resin and when the splice enters the elevated temperature zone of the wire tower.

The polyamide acid solution used in this example is prepared by dissolving 16.1 parts of benzophenone tetracarboxylic acid dianhydride in 74 ml. of N-methyl pyrrolidone in a three-neck, round bottom flask fitted with a thermometer, a stirrer and an air condenser protected by a calcium chloride tube. To the flask was added a solution of 13.4 parts of oxydianiline in 74 ml. of dimethylacetamide. The reaction mixture was held at 50 C. with stirring for 16 hours. The resulting polyamide solution which is applied to the splice has a Brookfield viscosity of 150 centipoises at 25 C.

EXAMPLE 2 Example 1 is repeated here except that the imide-forming polymer is the polymeric reaction product of pyromellitic di anhydride and methylene dianiline in N-methylpyrrolidone. The broken ends of the boron filament are brought into overlapping contact, coated, and dried according to the procedures described in example 1. A strong, heat resistant splice is obtained in less than 2 minutes.

EXAMPLE 3 This example is set forth here to illustrate the drawbacks encountered when using an epoxy resin system to splice the ends of a 4 mil diameter boron filament.

The epoxy resin system is prepared by mixing a small quantity of a commercial epoxy resin and an activator for the resin. This mixture is applied to the ends of the boron filament which are in overlapping contact. Heat is applied to the coated ends using an infrared heat lamp, for about 20 minutes in order to cure the epoxy and set the bond. After this time, the splice is advanced into the elevated temperature zone of the wire tower. While in the 400 C. zone, the splice fails.

Note that the commercial method described in example 3 has a further drawback in that the epoxy/activator system must be prepared in small quantities just prior to use wherein the imide-forming polymers used in the present invention have excellent shelf life at room temperature or below. Furthermore, the epoxy polymer is flammable and cannot be ignited so as to form a rapid bond as is the case with the imide-forming polymer solutions used in examples 1 and 2.

EXAMPLE 4 Example 1 is repeated here except that AWG 018 copper wire is spliced using the imide-forming solution and the procedures described in example 1 An excellent heat resistant splice is obtained in about 1 minute.

EXAMPLE 5 EXAMPLE 6 This example is set forth to illustrate the splicing of a 4 mil diameter boron filament using an imide-forming polymer solution which is prepared from a tricarboxylic component and a diamin'e component; This imide-forming polymer is prepared by thoroughly mixing trimellitic anhydride monoacid chloride (90.0 g., 0.43 mol) and methylene dianiline (86.4 g., 0.43 mol) in a reaction flask. A mixture of N-methyl pyrrolidone (210 g.) and triethylamine (43.2 g., 0.43 mol) is added with vigorous stirring. The solids dissolve rapidly and the temperature rises to about C. Stirring is continued for about 1 hour while the solution cools to about 50 C. At this point, the polymer solution is diluted with a mixture of N-methy] pyrrolidone (37 g.) and xylene 124 g). After standing overnight, the solution is filtered to remove the triethylamine hydrochloride and is diluted to about 20 percent solids with N methyl pyrrolidone.

This solution is then applied to overlapping ends of the boron filament and the solvent in the polymer solution is ignited and quenched as in example 1. A strong, thermally re sistant splice is obtained within 1 minute which withstands the elevated temperature of the wire tower (about 400 C.) within 2 minutes after the splice is made.

EXAMPLE 7 Example 6 is repeated here except that the imide-forming polymer is prepared by first reacting 2.1 moles of trimellitic acid anhydride with 1.0 mole ofp,p'-dihydroxyphenyl propane diacetate which reaction product is further reacted with diaminodiphenyl methane. The resulting polymer solution is then used to splice 4 mil diameter boron filament according to the procedure of example 1. A strong, thermally stable splice is obtained within 1 minute.

EXAMPLE 8 Example 1 is repeated here except that the imide-forming polymer solution is used to splice uncoated 4 mil diameter boron filaments that snapped while being wound on a takeup spool. The splicing procedure of example 1 is followed except that the splice is not subjected to the elevated temperatures of the wire-coating tower. The splice which was made within 1 minute is examined after 24 hours and compared to the heat cured splice of example 1. The respective splices are found to be comparable.

EXAMPLE 9 Example 1 is repeated here except that a heat gun is applied to the splice in order to evaporate the solvent and cure the polymer. A strong thermally stable splice is obtained in less than 4 minutes.

EXAMPLE 10 Example 1 is repeated here except that the infrared lamp of example 3 is used in order to evaporate the solvent and cure the polymer. A strong thermally stable splice is obtained in less than 5 minutes. This splice does not part when exposed to elevated temperatures of about 400 C in a wire tower.

EXAMPLE 11 Example 1 is repeated here except that a 10 mil diameter carbon fiber is spliced. A strong thermally resistant splice is obtained within 2 minutes.

EXAMPLE 12 Example 1 is repeated here except that a 10 mil graphite fiber is spliced. A strong thermally resistant splice is obtained within 2 minutes.

EXAMPLE 13 Example 1 is repeated here except that a refrasil fiber is spliced. A strong thermally resistant splice is obtained within 2 minutes.

The preferred thermally stable imide-forming polymers used to splice filaments in the practice of this invention are those prepared from aromatic tricarboxylic and tetracarboxylic components and aromatic polyamino compounds containing at least two amino groups per molecule. Especially preferred are those polymers prepared using benzophenone tetracarboxylic components and an aromatic primary diamine as are described in detail in U.S. Pat. Nos. 3,190,856 and 3,277,043.

By varying the type and amount of solvent in the polyimide solution the amounts of heat required to evaporate the solvent and effect a cure can be controlled as should be obvious to those skilled in the art.

Other heat sources other than the open flame, heat gun and infrared lamp used in the foregoing examples may be used to evaporate the solvent in the polymer solution and accelerate the cure of the imide-forrning resin. These would include ovens, hot plates, and other means which will become apparent to those skilled in the art.

If necessary, the ends to be spliced may be held in proximate position with respect to each other using holding means such as tape, clamps, jigs, etc., while the joint is coated with the imide-forming polymer and then while the polymer is cured. The holding means is then removed. A narrow shallow trough shape jig is especially useful for applying and curing the imide-forming polymer while maintaining the ends to be spliced in an overlapping position.

It should be noted that it is not necessary to keep the ends to be spliced in actual physical contact with each other unless the filament is to be used as an electrical or thermal conductor. For nonconductive applications the splice can be made as long as the ends are proximately positioned in respect to each other without the need for actual physical contact. However, those skilled in the art will readily realize that any space between the ends to be spliced should be kept to a minimum in order to provide a stronger bond and minimize the thickness of the splice.

The present invention is not limited to overlapping-type slices. It is equally applicable to butt and other type splices and can also be used to further bond or overcoat those splices made by twisting, tying, knotting, etc., the ends of the material to be joined wherever the nature of the materials to be spliced allow such physical manipulation.

From the foregoing, it will be realized that many variations may be made in the practice of the present invention without departing from the spirit and scope thereof.

What is claimed is:

l. A method of splicing thermally resistant filaments, fibers, threads, wires, strands and other related materials which comprises:

l. bringing the ends to be spliced into a proximate position with respect to each other,

2. applying an imide-forming polymer solution to the ends to be spliced,

3. curing the imide-forming polymer to a thermally stable polyimide wherein the curing of the imide-forming polymer is initiated by igniting the solvent in the imideforrning polymer solution.

2. The method of claim 1 wherein the imide-forming polymer is the polymeric reaction product of benzophenone tetracarboxylic acid dianhydride and an aromatic primary diamine.

3. The method of claim 1 wherein the imide-forming polymer is the polymeric reaction product of pyromellitic dianhydride and an aromatic primary diamine.

4. The method of claim 1 wherein the imide-forming polymer is the polymeric reaction product of monoacid halide trimellitic dianhydride and an aromatic primary diamine.

5. A method for splicing boron filaments which comprises:

1. bringing the ends to be spliced into a proximate position with respect to each other,

2. applying an imide-forming polymer solution to the ends to be spliced, and 2. curing the imlde-forming polymer to a thermally stable polyimide, wherein the curing of the imide-forming polymer is initiated by igniting the solvent in the imide forming polymer solution.

6. The method of claim 5 wherein the imide-forming polymer is the polymeric reaction product of benzophenone tetracarboxylic acid dianhydride and an aromatic primary diamine.

7. The method of claim 5 wherein the imide-forming polymer is the polymeric reaction product of pyromellitic dianhydride and an aromatic primary diamine.

8. The method of claim 5 wherein the imide-forming polymer is the polymeric reaction product of monoacid halide trimellitic dianhydride and an aromatic primary diamine. 

2. applying an imide-forming polymer solution to the ends to be spliced,
 2. The method of claim 1 wherein the imide-forming polymer is the polymeric reaction product of benzophenone tetracarboxylic acid dianhydride and an aromatic primary diamine.
 2. applying an imide-forming polymer solution to the ends to be spliced, and
 2. curing the imide-forming polymer to a thermally stable polyimide, wherein the curing of the imide-forming polymer is initiated by igniting the solvent in the imide-forming polymer solution.
 3. The method of claim 1 wherein the imide-forming polymer is the polymeric reaction product of pyromellitic dianhydride and an aromatic primary diamine.
 3. curing the imide-forming polymer to a thermally stable polyimide wherein the curing of the imide-forming polymer is initiated by igniting the solvent in the imide-forming polymer solution.
 4. The method of claim 1 wherein the imide-forming polymer is the polymeric reaction product of monoacid halide trimellitic dianhydride and an aromatic primary diamine.
 5. A method for splicing boron filaments which comprises:
 6. The method of claim 5 wherein the imide-forming polymer is the polymeric reaction product of benzophenone tetracarboxylic acid dianhydride and an aromatic primary diamine.
 7. The method of claim 5 wherein the imide-forming polymer is the polymeric reaction product of pyromellitic dianhydride and an aromatic primary diamine.
 8. The method of claim 5 wherein the imide-forming polymer is the polymeric reaction product of monoacid halide trimellitic dianhydride and an aromatic primary diamine. 